Generally, spinners are used to apply coatings of photosensitive material, commonly called photoresist, to substrates in semiconductor processes. This photoresist material is exposed to a selected pattern of ultraviolet light to control which areas will or will not be exposed during a subsequent step in the process.
Most integrated circuit processes use circular wafers for substrates and fabricate a few hundred chips on each wafer. After fabrication the wafer is diced and the individual circuits are separated.
Some applications have arisen wherein non-circular, generally oblong shaped, substrates of relatively large dimensions are employed to fabricate a particular device, for example, a thermal print head. In these applications it is particularly important to achieve uniform coverage of the substrate. Non-uniform coverage of the photoresist results in different areas of the device having different operating characteristics. For example, if one portion of a thermal print head operated at a higher temperature, a printout having an irregular appearance might be produced.
Previously, non-circular substrates have been held on top of circular spinner chucks by applied vacuum. This is the technique used for circular substrates. However, when using non-circular substrates, the aerodynamic properties of this structure, shown in FIG. 1, results in a build-up of coating material on the substrate as shown in FIG. 2.
In accordance with the preferred embodiment of the present invention, a recessed area for receiving the substrate is provided in a circular spinner chuck to alleviate the undesirable effects of the aerodynamic properties of a non-circular substrate.